The objective of this research is to increase understanding of Alzheimer's disease (AD), a common, important and disabling type of dementia. The investigations will focus on elucidating the characteristics and pathogenesis of the abnormal, neurofibrillary tangles that are a hallmark of the brain pathology of AD and which are of unknown origin and pathogenesis. Recently, our laboratory produced a monoclonal antibody, TI, against a partially purified, normal rabbit brain microtubule preparation (containing some neurofilament antigens). Up to half of the tangles in autopsy brain were labeled by this antibody. TI also decorated microtubules in cultured cells, but did not recognize neurofilament proteins. Preliminary studies with TI suggested that there may be a microtubule-related abnormality in AD. By utilizing the same antigen, 6 additional tangle-reactive monoclonal antibodies were produced. One resembled TI closely. Three immunolabeled large numbers of tangles and senile plaques. Of these, two recognized neurofilaments; none appeared to recognize microtubules. The present project will utilize these monoclonal antibodies to study human and animal tissues and cultured cells by light (LM) and electron microscope (EM) immunocytochemical and immunochemical methods. Initial emphasis will be placed on the antibodies that also labeled microtubules and on the antibody that decorated many tangles but not neurofilaments, because of their apparent uniqueness. The project aims to evaluate the relation between the paired helical filaments of tangles and the immunoreactive tangle constituents. Reactive tangles will be demonstrated by LM in semi-thin sections and then examined by EM in adjacent thin sections. Immunolabeling of tangles will be tested after extraction procedures to remove constituents other than paired helical filaments. Ultrastructural experiments will seek to localize the antibodies bound to tangle. The project also aims to assess the importance to AD of the antigens recognized by the monoclonal antibodies. It will compare the localizations of immunoreactivity in brain in AD and in other conditions. It will compare the localizations in brain to those in other tissues, in animals and in cultured cells. It will seek possible developmental, aging, or disease-related changes. Preabsorption and immunoblotting experiments will be done to study the specificities of the monoclonal antibodies and to characterize the normal antigens that are cross-reactive with tangles. The hypotheses underlying these studies are 1) that normal brain antigens, including a microtubule-associated antigen, may play roles in the pathogenesis of Alzheimer neurofibrillary tangles, and 2) that there may be a microtubule-related abnormality in AD.